1. Field of the Invention
The present invention relates to a method for producing a graft copolymer rubber and a polypropylene-based resin composition having excellent rigidity, impact resistance and flowability, containing said graft copolymer rubber. More particularly, the present invention relates to a method for producing a graft copolymer rubber in which an alkenyl aromatic compound is graft-polymerized to a specific ethylene-.alpha.-olefin-non-conjugated diene terpolymer rubber, and a polypropylene-based resin composition excellent in rigidity, impact resistance and flowability, containing said graft copolymer rubber.
2. Description of the Related Art
Recently, a polypropylene-based resin (e.g. propylene-ethylene block copolymer) is used for automobile materials and domestic electric appliances materials in view of lightness, low cost and the like. However, the conventional propylene-ethylene block copolymer material has low impact strength, and a high inorganic fillers content for obtaining excellent rigidity and thermal properties such as heat distortion temperature and the like, and therefore has a relatively high specific gravity.
It is proposed that, for improving impact strength, a graft copolymer rubber, in which an alkenyl aromatic compound is graft-polymerized to an ethylene-.alpha.-olefin-non-conjugated diene terpolymer rubber, is blended with a propylene-ethylene block copolymer. For example, in JP-A-57-135845 and JP-A-7-104466 propose, it is disclosed that the graft copolymer rubber produced in an aqueous suspension is mixed with a polypropylene-based resin. However, the graft copolymer rubber used has no suitable Q-value and Mooney viscosity, and the polypropylene-based resin into which the graft copolymer rubber is compounded has insufficient impact resistance and flowability.